1. Field of the Invention
The present invention relates to a thin-film transistor (TFT) substrate and a method of manufacturing the same, and more particularly, to a TFT substrate which includes TFTs having shorter channels and thus can be used in high-speed and ultra-high density & precision products and a method of manufacturing the TFT substrate.
2. Description of the Related Art
Liquid crystal displays (LCDs) are one of the most widely used types of flat panel displays (FPDs). Generally, an LCD includes a pair of substrates having electrodes and a liquid crystal layer interposed between the two substrates. In an LCD, voltages are applied to electrodes to generate an electric field. Accordingly, the alignment of liquid crystal molecules of a liquid crystal layer is determined, and polarization of incident light is controlled. As a result, a desired image is displayed on the LCD.
Of various types of LCDs, LCDs widely now used have electric field generating electrodes formed on each of two substrates. In particular, a plurality of pixel electrodes are arranged in a matrix form on one (a thin-film transistor (TFT) substrate) of the substrates, and a common electrode covers the entire surface of the other one (a common electrode substrate) of the substrates. To display an image on these LCDs, a separate voltage must be applied to each pixel electrode. Thus, TFTs, each being a three-terminal device for switching a voltage that is to be applied to each pixel electrode, are connected to the pixel electrodes, respectively, and gate lines and data lines are formed on one of the substrates. Here, the gate lines deliver signals for controlling the TFTs, and the data lines deliver voltages that are to be applied to the pixel electrodes.
In the case of high-speed and high density & precision LCDs, each pixel must be charged to a desired voltage level during a short horizontal period (1H). To this end, ON current of each TFT needs to be improved. The ON current of each TFT can be improved by increasing a ratio (W/L) of a width (W) of a channel region to a length (L) thereof. In theory, the width (W) of the channel region can be increased unlimitedly. However, a wider channel region increases the size of each TFT, thereby reducing an aperture ratio and increasing parasitic capacitance. Consequently, screen display quality is significantly reduced. Meanwhile, the length (L) of the channel region can no longer be reduced due to limitations of exposure facilities.